Abstract：Urban road runoff caused by 32 storm events were collected proportionally to the total volume and completely through the rainfall time at south second ring road in Xi’an City using self-made volume proportional collecting device from March 2009 to February 2010. Event mean concentration (EMC) of SS, NH3-N, total and dissolved COD, Pb and Zn were tested. Pollution intensity, mode of occurrence, relationship, concentration influential factors, as well as seasonal variation of runoff pollutants were explored. The results showed that EMC of main runoff pollutants varied greatly and the median EMC of SS, COD, dissolved COD, NH3-N, Pb, Zn and dissolved Zn were 1543, 574, 129, 1.86, 0.042, 0.219, 0.111mg/L respectively. The coefficient of variation ranged from 0.41 to 0.8. The median EMC of SS and COD were far greater than the values of Integrated Wastewater Discharge Standard Grade III, so SS and COD were the main pollutants of road runoff. The occurrence of Pb was mainly granular state and 47.4% of Zn, 25.1% of organic pollutants was dissolved. The correlation of COD, Pb and Zn with SS were significant at 0.01 level and the correlation coefficients were 0.845, 0.807 and 0.903 respectively, which showed that particulate matters were carrier for many other pollutants. The descending order for influence weights of rainfall characteristics on concentration of pollutants was as follows: rainfall volume> maximum rainfall intensity > rainfall duration. Antecedent dry period (ADP) had no correlation with EMC of many pollutants except dissolved Zn and dissolved COD. Result of one factor analysis of variance showed that EMC of SS, COD and NH3-N varied with seasons significantly, while the variation tendency of other pollutants, such as dissolved COD, Pb and Zn was not obvious.
